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13 May 2021

What Are Flowering Hormones and How Should They Be Used?

Like humans, cannabis plants produce hormones throughout their life cycle, though much about them remains a mystery. These hormones are endogenous chemical messengers that influence plant biology to spur on various changes, such as the beginning of flower production as the plant reaches the bloom phase. Also, like humans, these hormones cause dramatic changes in your plants as they play their role in the development of foliage, stalks, and buds.

Different hormonal compounds are produced at various stages throughout a plant’s development, and an understanding of these compounds allows the grower to supplement or omit certain hormones as necessary. This is crucial when working with short-day plants such as marijuana, which begin flowering as the day length shortens to twelve or fewer hours.

Depending on the strain, climate and method, hormone supplementation may be necessary to achieve maximum yields. Because these hormones can so drastically affect your plant’s growth and timing, a working understanding of plant hormones is essential for a successful grow.

The Flowering Hormones

Though there is still much research to be conducted in the field of plant hormones, there is enough to know which plant hormones can positively and negatively influence plant behaviour and growth during the bloom stage. Let’s examine some of the more common flowering hormones, what they do, and how they should be used when applied by a grower.

Gibberellic Acid

Gibberellic acids, also commonly known as gibberellins, are plant hormones that play an important role throughout the life cycle of a cannabis plant. In the plant’s earliest stages, gibberellic acid plays a role in ending seed dormancy and spurring on germination, as well as transitioning the plant from apical meristem growth to shoot development.

Gibberellins can be thought of as growth accelerators. Their presence increases cell elongation and cell division, the result of which is increased growth of plant tissue leading to stem elongation, greater distance between internodes, and a plant physiology that generally resembles a male plant. In addition, gibberellic acids play a significant role in sex differentiation of plants, as well as delaying and slowing flowering.

Gibberellic acids should be applied by foliar spray carefully and in low concentrations during the vegetative phase to delay flowering, but the grower should be aware that its application will inevitably lead to the plant stretching, or developing long shoots, once the plant has begun flowering. This can lead to issues for growers working in small spaces. Gibberellic acid can be found easily online or in a hydroponic shop or nursery.

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Florigen

Though much remains unknown about the flowering hormone florigen, we do know that it plays a significant role in the triggering of flower formation and the onset of the flowering period. Florigen, known as a general growth hormone, has been determined to play a factor in the flowering of all flowering plants, and cannabis is no exception.

Florigen is produced in the plant’s leaves, and its transmission to the apical meristem is triggered by changes in photoperiod, known as photoperiodic induction. Florigen acts upon the apical buds and growing tips, indicating to them that it is time to begin flower production.

Florigen is typically found in fertilizers particularly formulated for inducing flowering. These may differ from typical “bloom” fertilizers as these tend to be base nutrients, supplying plants with necessary nutrition rather than hormones. Instead, you’ll find florigen in products that promise to spur on early flowering.

Additionally, florigen levels can be manipulated through various pruning techniques, such as topping or fimming, which can redistribute the hormone to various apical buds and tips rather than focusing all of it on one main apical tip.

Auxin

Auxins are plant hormones that can be thought of as plant growth regulators, influencing both the plant’s foliage and root system. Auxins influence cell division and cell elongation by softening cell walls. Mainly known as an inhibitor of plant growth, its presence in the apical meristem inhibits the growth of side shoots; this growth pattern is referred to as apical dominance.

Removal of the apical tip will cause auxin to be redistributed throughout the plant’s phloem, leading to the development of side shoots and lower bud sites, one of the primary benefits to practices like topping and fimming.

Though auxin’s role is primarily in the development of the plant and its stature, it also plays a minor role in inducing flowering and the development of a plant’s sex organs, as well as delaying the deterioration of buds (known as senescence).

Typically, auxins are used in the early stages of plant growth to promote root growth on clones and are most commonly found in rooting gels. The most common form of auxin is indole-3-acetic acid, or IAA, biosynthesized in the apex and young leaves of plants but readily available as a cloning solution from many suppliers.

Cannabis plant flowering thanks to plant hormones

Ethylene

Ethylene is structurally the simplest plant hormone. Its use in agriculture can be traced back to ancient Egypt, where figs were scored to promote ethylene production and thus, decreased fruit ripening times. Aside from aiding in the ripening of fruits and flowers, ethylene also stimulates flower opening and causes the shedding of leaves toward the end of the lifecycle.

Used worldwide in agricultural production, ethylene can hasten the bloom cycle of flowering plants such as cannabis, resulting in smaller plants but quicker harvests.

Plants can be significantly affected by high concentrations of ethylene. It is so potent that it is measured in parts per billion (PPB) in the air, with as little as 10 PPB causing mutations. Ethylene can be supplemented if necessary, but most often, ethylene products are focused on absorbing excess ethylene rather than generating it.

Cytokinin

Cytokinins are hormonal compounds which are primarily responsible for cell division. In cannabis plants, cytokinins are known to help plant cells multiply, leading to the formation of side shoots and buds. In this way, cytokinin acts almost as the antithesis of auxin, which promotes apical growth. The removal of the apical meristem increases cytokinin production throughout the plant, leading to bushier, fuller plants with more bud sites.

Cytokinin supplementation will lead to larger, broader leaves which leads to a greater number of stomata, and thus, increased transpiration of water and nutrients. Additionally, the increased surface area of the leaves promotes enhanced photosynthesis, leading to healthier and more productive plants. Though there are over 200 cytokinins that have been classified, the most commonly used include gibberellins, kinetin and brassinolide, also known as the “steroid” of plant hormones.

Abscisic Acid

Abscisic acid, also known as ABA, goes through synthesis partially in the chloroplasts of a plant, and it is typically released when the plant goes through stress. ABA is responsible for the closing of stomata when a plant receives too little water or other types of stress. Originally thought to be responsible for the abscission (or shedding) of leaves and fruit, it was later discovered that those processes are more closely related to ethylene production and release.

Making Use of Flowering Hormones

Though the hormones listed here are by no means the complete list of plant hormones that will affect your marijuana garden, an understanding of these few basics will go a long way. The interactions of these hormones play an interesting role in plant development, as well, so true mastery of hormonal basics may take a significant amount of trial and error.

When working with plant hormones, it’s always best to administer small doses first to ensure that your plants don’t experience an adverse reaction. It’s also important to remember that unlike overfeeding with nutrients, overdosing with hormones can be fatal to your plants.

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Post author
Michael Richey
Michael loves to grow cannabis and write about what he learns along the way. His best friends are his dogs and marijuana.
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